My wallet is nowhere to be found.I ( )when I was on the bus

问题描述:

My wallet is nowhere to be found.I ( )when I was on the bus
A.must drop it B.should have dropoed it C.must have dropped it D.had dropped it

答案选C.must have dropped it
本句意为:我的钱包到处都找不到.肯定是在车上的时候,我把它弄掉了.
对过去情况的肯定推测,用must have done,所以选C.